The present invention relates to a venturi configuration forming part of the main fuel injector in a combustor for a gas turbine and particularly relates to a venturi diffuser configuration affording a uniformity of the fuel/air mixture downstream of the fuel injector and at the catalyst inlet.
In certain fuel gas injectors for combustors in a gas turbine, there are provided a plurality of closely spaced parallel venturi tubes disposed in a pair of spaced apart header plates. The header plates and the venturi tubes form a plenum into which pressurized fuel is supplied and from which fuel is supplied through orifices into the venturi tubes to the interior of the tubes for mixing with high velocity air streams passing through the venturi tubes. In prior fuel injection systems of this type, for example, see U.S. Pat. Nos. 4,845,952 and 4,966,001, the combined flow from the venturi tubes mixes downstream prior to entry into the catalyst inlet plane. The prior venturi tubes are generally of circular cross-sectional configurations and have substantial gaps at the exit plane of the diffusers between the circular diffuser exits. While the fuel/air mixing occurs within the venturis and the venturis complete the combustor cross-section, mixing also occurs in the downstream region between the venturi exit plane and the catalyst inlet. Because of the large recirculation regions that form in the wake of the inter-venturi gaps, it has been found that the flame holding resistance has diminished. Accordingly, there is a need for improved fuel/air mixing, particularly downstream of the venturi tubes, to insure a uniformity of the fuel/air mixture across the entire cross-section of the catalyst inlet.